Update documentation on demo app to show double quotes around custom properties

[juwara0]

In this block of text on the demo app the resource=event should be updated to resource="event"

Using the same Behavior data from the previous example and the following in the template:

{{#sl-able activity="create" resource=event possible=false}}

Creating an event is not possible

{{/sl-able}}

{{#sl-unable activity="reschedule" resource=event possible=false}}

Rescheduling an event is not possible

{{/sl-unable}}

[juwara0]

@notmessenger: I am working this